Conventionally, containers or vessels in which a latent heat accumulating material is enclosed for use in greenhouses, solar heat water heaters, etc. are presented in cylindrical, spherical or box-like configurations, and much labor and troublesome procedures have been required for installing these enclosing containers in a wide range of large areas. Meanwhile, as a result of various experiments carried out so far, it has been made clear that configurations of capsules for the cylindrical, spherical or box-like containers in which the latent heat accumulating material is enclosed, should desirably be those having a large surface area, and also a small thickness of the latent heat accumulating material (i.e. a distance from a heat conducting surface to a center of the container) so as to expedite heat transfer of the heat accumulating material accommodated therein. Accordingly, in the case of a container, for example, of a spherical shape, in order to reduce its diameter and yet, to maintain a predetermined amount of heat accumulation, it has been necessary to increase the number of capsules by that extent, thus resulting in increased cost and consequent high prices.